Ziegler-Natta catalyst systems can be used for stereospecific polymerization of olefins, which can include a solid catalyst component, with an alkylaluminum compound. The solid catalyst component can be made from or contain a titanium compound an an internal electron donor compound, both supported on a magnesium dihalide. The catalyst system can also include an external donor. This catalyst systemcan prepare, propylene polymers with high isotacticity and xylene insolubility. With relatively high porosity, these catalyst systems can be used to prepare high impact heterophasic copolymers made from or containing a crystalline propylene polymer and a very low crystalline, highly xylene-soluble in ethylene-based copolymer. To achieve these heterophasic copolymers, there is a need that the catalyst prepare the low crystallinity copolymer without clogging, forming chunks, agglomerating particles, or adhering to reactor walls.
Unfortunately, an increase in the catalyst system's porosity may decrease the catalyst system's polymerization activity and isospecificity. To address the loss in isospecificity, additional amounts of external donors can be required; however, the increase of external donors can further harm the catalyst's activity.
It would be therefore general interest the possibility of increasing the intrinsic capability of these solid catalyst components to produce stereoregular polymers. In fact, an intrinsically more stereospecific catalyst component would allow to use a lower amount of stereoregulating external donor to reach the target of polymer xylene insolubility and this, in turn, would be translated into the possibility of obtaining a higher plant productivity.
In U.S. Pat. No. 4,613,655 substantial amounts (30% by weight or higher) of different inorganic compounds and, among them Cu2Cl2 (table VII), is mixed with MgCl2 and then ground in the presence of TiCl4 in order to produce a catalyst. Apart from the effect of dilution of MgCl2, the catalyst, used in the ethylene polymerization, did not show any improvement from the presence of Cu2Cl2. The catalysts have negligible porosity.
JP2010-155949 discloses the preparation of solid catalysts components according to several techniques all of them having in common the use of copper chlorides at various stages of preparation. According to this reference, the catalyst components containing Cu allows to increase the catalyst activity while the stereospecificity is maintained at the same level of the comparative catalyst (not containing Cu) or slightly increased. The catalyst have low and insufficient porosity.
Now the applicant has surprisingly found that it is possible to increase the stereospecificity of porous catalyst components based on Mg containing support on which are supported titanium atoms and donors by modifying it with Cu oxide compounds.